Abstract
Cage-type mesoporous silicas display rich structural diversity. Among them, cage-type mesoporous silicas with tetrahedrally close-packed (TCP) structures can be described by four types of polyhedron, 512, 51262, 51263, and 51264. We have investigated (i) the Fm3m-Fd3m type intergrowth and (ii) several types of stacking fault in the Fd3m structure using transmission electron microscopy (TEM). The stacking faults can be explained by the stacking of three kinds of layer based on a description of the polyhedra. We have also observed that (iii) one of new stacking sequences, with a large repeating unit, contains these three layers and bears a close resemblance to one of the Frank-Kasper phases with rhombohedral symmetry known as μ-phase.
